Just wanted to contribute as I'm forever on the hunt for good quality clothes that fit well.
For reference I'm 5ft1, 45kg, 32a.
Hobbs is disappointing. I was so happy when I discovered that they had a petite range and bought one of the wool camel coats in size 6. The fit was just off, the proportions were all wrong. I think it may have been better for someone who was 5ft4 or 5 with longer arms. Anyway, tried again with the trench. Nope. I don't think they can call their stuff petite, it's not!?
J Crew I love, I have several of their coats although the quality isn't as great as a few years ago, but the fit is spot on. The 00P coats fit me like a glove. Their trousers are also absolutely the perfect fit. So I really, really recommend J Crew for clothes that look like they're tailored to your body.
Everlane - Really quite good despite not having a petite line. I've probably made 10 orders in the past year, returned very few things. Some of their trousers come in ankle length and fit me well in every way and don't just look like tall people's cropped trousers. The tops are petite friendly. Jackets not quite the most perfect fit though.
Boden - I think I've tried several of their trousers, most recently the corduroy ones. None of them fit me. The waist is absolutely massive, weirdly so relative to the legs. Cropped cardigans are not bad.
Just recently been getting into Sezane - They do a size 2 in shoes which is brilliant. Bought a pair of boots recently and was very pleased with the quality. Just bought a couple of sweaters in size XS, will report back. But I've tried on one fo their blouses - The Ann blouse in size 6, it was massive and in no way petite friendly unless you roll up sleeves and tuck it in. Also why do the models have every single top tucked in??!! I want to see the hem, Sezane!
Cos - Hit and miss. I had a lovely wool jumper from there many years ago and it actually fit me. The t-shirts also fit me but other things are probably better for taller people. Bodysuits are too long.
Just bought a jumper from Toast and now I'm worried it will be too big...